Bidirectional Optical Time Domain Reflectometer using a single wavelength

Abstract

An Optical Time Domain Reflectometer (OTDR) includes a transmitter configured to transmit first OTDR pulses, at a first pulse period and at a wavelength λ, over a fiber under test; a receiver configured to receive signals from the fiber under test; and circuitry configured to set the first pulse period and to average measurements resulting from the received signals, wherein the OTDR is configured to operate with a second OTDR at another end of the fiber under test for a bidirectional OTDR measurement, wherein the second OTDR uses the same wavelength λ and transmits second OTDR pulses at a second pulse period, different from the first pulse period.

What is claimed is: 
     
         1 . An Optical Time Domain Reflectometer (OTDR) comprising:
 a transmitter configured to transmit first OTDR pulses, at a first pulse period and at a wavelength λ, over a fiber under test;   a receiver configured to receive signals from the fiber under test; and   circuitry configured to set the first pulse period and to average measurements resulting from the received signals, wherein the OTDR is configured to operate with a second OTDR at another end of the fiber under test for a bidirectional OTDR measurement, wherein the second OTDR uses the same wavelength λ and transmits second OTDR pulses at a second pulse period, different from the first pulse period.   
     
     
         2 . The OTDR of  claim 1 , wherein the OTDR is one of integrated in a module in an optical network element and a pluggable module configured to operate in the optical network element, such that the OTDR is an embedded OTDR. 
     
     
         3 . The OTDR of  claim 1 , wherein the wavelength λ is outside of a range of wavelengths used for traffic-carrying channels in an optical line system. 
     
     
         4 . The OTDR of  claim 1 , wherein the first pulse period and the second pulse period are selected so that any interfering second OTDR pulses are spread across the first pulse period. 
     
     
         5 . The OTDR of  claim 1 , further comprising
 a clock utilized by the transmitter for the first pulse period, wherein the clock is within a tolerance of a second clock at the second OTDR.   
     
     
         6 . The OTDR of  claim 1 , wherein the first pulse period is selected without coordination with the second OTDR. 
     
     
         7 . The OTDR of  claim 1 , wherein the first pulse period is selected based on whether the transmitter is configured to transmit the first OTDR pulses co-propagating or counter-propagating with traffic-carrying wavelengths. 
     
     
         8 . The OTDR of  claim 1 , wherein the first pulse period and the second pulse period are assigned based on a global assignment that ensures adjacent nodes have different pulse periods. 
     
     
         9 . The OTDR of  claim 1 , wherein the first pulse period and the second pulse period are assigned based on connectivity to adjacent nodes. 
     
     
         10 . The OTDR of  claim 1 , wherein the first pulse period and the second pulse period are assigned based on a pulse width of the first and second OTDR pulses and based on a distance of the bidirectional OTDR measurement. 
     
     
         11 . A bidirectional Optical Time Domain Reflectometer (OTDR) method comprising steps of:
 transmitting OTDR pulses from each end of a fiber under test, at a same wavelength λ from both ends and with a first pulse period at one end and a second pulse period, different from the first pulse period, at the other end;   receiving signals from the fiber under test at both ends; and   averaging, at both ends, measurements resulting from the received signals at both ends.   
     
     
         12 . The bidirectional OTDR method of  claim 11 , wherein the transmitting and the receiving are performed by one of a module integrated in an optical network element and a pluggable module configured to operate in the optical network element, for an embedded OTDR. 
     
     
         13 . The bidirectional OTDR method of  claim 11 , wherein the wavelength λ is outside of a range of wavelengths used for traffic-carrying channels in an optical line system. 
     
     
         14 . The bidirectional OTDR method of  claim 11 , wherein the first pulse period and the second pulse period are selected so that any interfering OTDR pulses are spread across the first pulse period. 
     
     
         15 . The bidirectional OTDR method of  claim 11 , wherein the steps further include operating a clock at each end, wherein the clock at each end is within a tolerance of one another. 
     
     
         16 . An apparatus comprising circuitry configured to:
 cause transmission of first Optical Time Domain Reflectometer (OTDR) pulses at a first pulse period and at a wavelength λ, over a fiber under test, and   responsive to received signals from the fiber under test, average measurements resulting from the received signals, wherein the first OTDR pulses are configured to operate with a second OTDR at another end of the fiber under test for a bidirectional OTDR measurement, wherein the second OTDR uses the same wavelength λ and transmits second OTDR pulses at a second pulse period, different from the first pulse period.   
     
     
         17 . The apparatus of  claim 16 , wherein the circuitry is one of integrated in a module in an optical network element and a pluggable module configured to operate in the optical network element, as an embedded OTDR. 
     
     
         18 . The apparatus of  claim 16 , wherein the wavelength λ is outside of a range of wavelengths used for traffic-carrying channels in an optical line system. 
     
     
         19 . The apparatus of  claim 16 , wherein the first pulse period and the second pulse period are selected so that any interfering second OTDR pulses are spread across the first pulse period. 
     
     
         20 . The apparatus of  claim 16 , further comprising
 a clock utilized for the first pulse period, wherein the clock is within a tolerance of a second clock at the second OTDR.